(1) Field of the Invention
The present invention relates to a method of manufacturing a nickel hydroxide electrode of the sintered type for use in an alkaline storage cell, in which a porous nickel sintered plaque is filled with active materials by impregnating the sintered plaque with an acid nickel salt such as nickel nitrate, and thereafter subjecting it to an alkali treatment.
(2) Description of the Prior Art
A conventional method of manufacturing a nickel hydroxide electrode of the sintered type for use in an alkaline storage cell employs an active material filling operation. In this operation, a porous nickel sintered plaque to act as a support for an active material is immersed in a solution of an acid nickel salt such as nickel nitrate to impregnate pores of the sintered plaque with the nickel salt, and thereafter the nickel salt is activated by changing it into nickel hydroxide through contact with alkali solution. However, one such active material filling operation cannot fill the nickel sintered plaque with a sufficient amount of active material. This operation must be repeated several times to fill the sintered plaque with a sufficient amount of active material, which results in a low efficiency of active materials filling work.
In order to improve the active materials filling efficiency and simplify the manufacturing process, a molten salt solution such as a high temperature and high concentration aqueous solution of nickel nitrate is used to obtain a necessary amount of active material through a reduced number of impregnating steps. In this case, however, the impregnant solution naturally is highly corrosive and the sintered plaque is thereby corroded. Consequently, the nickel forming the sintered plaque becomes dissolved to embrittle the electrode. The cell incorporating such an electrode has a reduced cycle performance.
On the other hand, Japanese patent publications kokai Nos. 59-78457 and 59-96659 have proposed a method of preventing the corrosion of the sintered plaque by forming oxidation-resistant nickel oxide on surfaces of the nickel sintered plaque in the presence of oxygen and at high temperature. According to this method, however, the corrosion of the sintered plaque cannot be checked sufficiently if nickel oxide is formed in a small amount. On the other hand, if an increased amount of nickel oxide is formed in an attempt to obtain satisfactory results, the conductivity between the active material and sintered plaque will be seriously impaired since nickel oxide has a poor conductivity. This gives rise to the problem of lowering the utilization factor of the active material.